The overall performance of instrumentation or computer systems used for evaluating cardiac function is obviously limited by the quality of the signals on which diagnostic measurements are made. Signal quality can be maximized by interactive preprocessing during data acquisition. To accomplish this goal a preprocessor must be able to obtain, transform, and test the signal. We propose to systematically study the problem of digital preprocessing of both the electrocardiogram, which is a universal input in cardiovascular diagnosis, and the echocardiogram, which has become an established diagnostic procedure in clinical cardiology. The electrocardiogram and echocardiogram are of interest because they yield independent and complementary information, are noninvasive, and are suitable for automatic analysis. The electrocardiogram preprocessor will be designed to condition a short segment of three simultaneous leads for subsequent automatic off-line analysis by an established interpretation program. It will automatically control gain and calibration, limit artifact by rejecting records of poor technical quality, and correct procedural errors by alterting the technician to measurement inconsistencies. The echocardiogram preprocessor will transform ultrasonic echoes from a single transducer into a time-motion display in which each interface of interest is characterized by a single-valued function of time. The resultant display will be enhanced compared to that of conventional instrumentation and the signal will be in a format suitable for subsequent measurement. We plan to implement both preprocessors in a single microcomputer-based system. Because the microcomputer system is specially tailored for preprocessing and is built around an inexpensive central processing unit, it will offer important cost advantages over conventional computer techniques. The trend in microcomputer development suggests that ultimately all processing can be economically carried out at the data acquisition site. The proposed preprocessor is an important step toward that objective.